Well structure and method for protecting permafrost

ABSTRACT

Permafrost about a bore, such as an oil well is protected by surrounding the casing of the well with an insulating layer, surrounding the insulating layer with a hollow jacket, the jacket containing liquid boiling below the freezing point of the permafrost. The boiling liquid being condensed adjacent the upper portion of the jacket and the liquid returned downwardly in the jacket.

United States Patent [191 [11 1 3,771,590 [451' Nov. 13, 1973 Best et al.

[ WELL STRUCTURE AND METHOD FOR [56] References Cited PROTECTING PERMAFROST UNITED STATES PATENTS Inventors: John 8. Best, Midland, h; J hn 3,662,832 5/1972 K6618! eLal. 165/45 Larry Duda, State College, Pa. [73] Assignee: The Dow Chemical Company, P i ry i -C es 511 310 Midland, Mi h, Attorney-William M. Yates et al.

[22] Filed: Dec. 20, 1971 57 ABSTRACT [21] Appl. No.: 210,037 1 Permafrost about a bore, such as an oil well is pro- Related Applicatmn Dam tected by surrounding the casing of the well with an [63] Continuation-impart of Ser. No. 112,634, Feb. 4, insulating layer, surrounding the insulating layer with 1971, abandoneda hollow jacket, the jacket containing liquid boiling below the freezing point of the permafrost. The boil- [52] US. Cl 1.65/1, 165/45, 165/105 ing liquid being condensed adjacent the upper portion [51] Int. Cl. F28d 15/00 of the jacket and the liquid returned downwardly in [58] Field of Search 165/105, 45, l, 117, th j k t,

5 Claims, 4 Drawing Figures i I; v J r n R a 2 x l3 1 l' 7 1% 2 h 18 M .2 w J ":--J .A ,d- 24 q 'Q 2 7 a, 55 A z 1 K7 :7

Patented Nov. 13, 1973 YPJ/ w m w w H% ww/ i 6 8 WELL STRUCTURE AND METHOD FOR PROTECTING PERMAFROST This application is a continuation-in-part of our copending application Ser. No. 1 12,634, filed Feb. 4, 1971, now abandoned.

Substantial difficulty is encountered when removing subterranean fluids such as oil from a well penetrating a permafrost layer. Generally the fluid such as oil is at a temperature substantially above the melting point of water and can quickly cause melting of the permafrost adjacent the well. Such melting is very undesirable from a mechanical standpoint. Generally in sinking such a well, conventional mechanical refrigeration has been employed to maintain the permafrost immediately adjacent the uppermost portion of the well. However, such conventional refrigeration techniques usually are not satisfactory for maintaining permafrost conditions about a well for an extended distance such as distances in excess of 100 feet and several hundreds of feet.

It would be desirable if there were available an improved device for maintaining permafrost about a well bore.

It would also be desirable if such a method and device would operate with relatively simple equipment.

lt would alsobe desirable if such a method and device were operable with minimal maintenance.

These benefits and other advantages in accordance with the present invention are achieved in a method for maintaining permafrost about a well bore or conduit, the steps of the method comprising, providing a well conduit extending downwardly in the earth through a permafrost layer, surrounding the conduit at least in the upper region of the permafrost layer with a thermally insulating layer, disposing generally about the insulating layer a hollow elongate housing defining therein a chamber, disposing within the chamber a low boiling liquid, the liquid boiling at least 0.lF. below the freezing point of thepermafrost, removing a heated vapor of the liquid upwardly through the conduit thereby heating the low boiling liquid within the elongate chamber to its boiling point, condensing the liquid at a location generally adjacent the upper surface of the permafrost and returning the liquid downwardly within the chamber.

Also contemplated within the present invention is a well structure, the well structurecomprising a well conduit extending downwardly into the earth through a layer of permafrost and a thermally insulating layer disposed about the conduit at least adjacent to the uppermost portion of the permafrost, a housing defining an inner chamber disposed generally about the thermally insulating layer and vapor condensing means in operative association with the housing, and disposed generally adjacent the uppermost portion thereof.

Further features and advantages of the present invention will become more apparent from the following specification taken in connection with the drawing herein.

FIG. 1 is a partly in section schematic representation of a well in accordance with the present invention.

HO. 2 depicts an alternate condensing means suitable for use with the present invention.

FIG. 3 depicts an alternate embodiment of a chamber suited for use in the present invention.

FlG. 4 depicts an alternate liquid distributing means.

In FIG.1 there is schematically shown a partly in section view of a well in accordance with the present invention generally designated by the reference numeral 10. The well 10 comprises a casing or conduit 11. Conduit 11 has an upper end 12 and lower end 13a. Conduit 11 comprising a first or outer conduit 13, the second or inner conduit 14.

t A generally annular insulating layer 16 surrounds the casing 11. Beneficially, the insulating layer 16 is a low thermal conductivity cement such as an air entrained cement. Advantageously adjacent the surface where installation pressures are low, synthetic resinous foams may be employed as the insulating layer. The insulating layer 16 extends generally from a location adjacent the first end 12 of the casing 11 downwardly toward the second end 13 of conduit 11 to a desired depth into or beyond permafrost 18a. The insulation 16 is generally coaxial with conduit 11. A housing 18 having a generally annular configuration is disposed about the insulating layer 16. The housing 18 comprises a first or inner wall 19 and a second or outer wall 20. The walls 19 and 1 20 are spaced apart to form an elongated generally annular chamber 22 which is generally coextensive with the housing 18. Affixed to the inner wall 19 of the housing 20 and extending outwardly therefrom into the chamber 22 are a plurality of liquid retaining means or troughs 24. Each of the troughs 24 defines a generally upwardly facing annular recess 26 adapted to receive I and maintain a liquid. The walls 19 and 20 are joined in sealing relationship to an upper end 27 of the housing 18 and at a lower end 28 of the housing 18.

A low boiling liquid 31 is disposed at the lower end 28 of the housing 18 within the chamber 22. Portions of the liquid 31 are also disposed within the annular recess 26 of the trays or retaining means 24. A liquid vapor condensing means 35 is in operative communication with the upper end 27 of the housing 18 and adapted to receive vapors of the liquid therefrom by means of a conduit 37. A seal and pressure regulating means 38 is in operative communication with the chamber 22 via the conduit 37. Also in communication with the chamber 22 is a liquid return line or conduit 41 adapted to return liquid from the condensing means 35 and discharge it against the inner wall 19 of the housing 18. The housing 18 is surrounded and sealed at the lower end 28 by a cementitious or insulating layer 43. Adjacent the upper end 12 of conduit 11 and external to the insulating layer 43 is a refrigerated casing 45 which beneficially is employed to initially stabilize the permafrost for the initial installation of the well. A cementitious layer 46 surrounds the casing 45 and beneficially is of similar composition to layer 43.

In operation'of the wellin accordance with the present invention a suitable volatile liquid such as the liquid 31 is added to the chamber 22 and the pressure regulating means 38 which is depicted as a hydraulic leg is adjusted to provide a pressure such that the boiling point of the liquid is from about 14, to 301F.

Suitable liquids for use in the present invention are materials such as dichlorodifluoromethane, sulfur dioxide, ethylchloride, trichlorofluoromethane, a 1:1 mixture of methyl bromide and methylchloride. Beneficially by employing such liquids the pressure within the chamber 22 can be maintained from about 5-25 pounds per square inch absolute and conventional pressure equipment avoided. Generally it is desirable to operate at atmospheric pressure to assure a relatively constant boiling point of the liquidand assure cooling and avoid a pressure relief valve which may malfunc' tion at a time when the well is unattended. Generally the deeper the jacket or housing 18 the lower the boiling liquid will be employed and the shorter or shallower the jacket higher boiling liquid compositions are employed. As fluid is withdrawn from the well through conduit 1 1, some heat is lost to the first insulating layer 16. The insulation 16 does not transmit a large amount of heat relative to the heat available from the conduit 1 1. The temperature of the inner wall 19 of the housing 18 is raised to the boiling point of the liquid 31. As the liquid 31 boils in the bottom 28 of the housing and in the annular retaining means 24, heat is absorbed from the wall 19 and insulation 16, and the vapor passed upwardly through the conduit 37 to the condensing means 35 where heat is removed and the resulting liquid passed through conduit 41 and to the inner wall 19 of the housing 18. Liquid flowing downwardly over the wall 19 enters and fills the liquid retaining means 24 whereupon the liquid overflows and fills the next lower retaining means and eventually replenishes the liquid in the bottom 28 of the housing 18. As the boiling point of the liquid is maintained below the freezing point of the permafrost, heat is drawn from the permafrost through the insulating layer 43, and the permafrost maintained or even increased depending upon the desired operating conditions.

The condensing means 35, conveniently for winter season operations, is an air cooled condenser wherein the ambient air at sub-freezing temperatures beneficially serves to remove heat from the vaporized liquid. When ambient air temperatures such as in the summer season are above the condensing temperature of the liquid beneficially mechanical refrigeration is employed to remove heat from the condenser. Thus throughout the annual ambient temperature cycle adequate condensation of the low boiling liquid is maintained.

In FIG. 2 there is depicted an alternate embodiment of the invention generally designated by the reference numeral 50. The embodiment 50 has a conduit 51 surrounded by an annular jacket 52 of generally similar construction to the housing 18 of FIG. 1. A conduit 53 is in operative communication with the chamber 18 and provides a liquid condensing means. The conduit 53 is enclosed within a liquid retaining chamber 54. The chamber 54 is in turn enclosed within a thermally insulating housing 55. The chamber 54 has a vent 56 adapted to vent gases therefrom. Beneficially the embodiment of FIG. 2 is of particular benefit when ambient air is often above the condensing temperature of the liquid for significant periods of time. A cryogenic liquid such as liquefied natural gas or liquid nitrogen is added to the chamber 54 to provide the desired cooling. Beneficially the housing 52 is separately vented to the atmosphere by means not shown.

In FIG. 3 there is depicted an alternate embodiment of the invention generally designated by the reference numeral 60. The embodiment 60 shows a sectional view of an outer wall 61 of a housing such as the housing 18 of FIG. 1. The wall 61 has an inner curved surface 62. A trough 63 is helically disposed on the wall 62. The wall 62 and the trough 63 define a liquid flow channel 64, which helically descends from the upper portion of the housing 60 to the lower portion thereof. The trough 63 has a plurality of liquid retaining means 65. The liquid retaining means 65 are cup-like depressions formed in the lowermost portion of the trough 63.

Conveniently, such retaining means may have almost any desired configuration, for example, transverse serrations in the floor of the trough 63 or they may be formed by periodically reducing the downward pitch of the spiral of the trough to provide the small regions of reversed pitch.

In FIG. 4 there is depicted an alternate liquid return means generally designated by the reference numeral 70. The return means is disposed within a chamber such as the chamber 22. The liquid distributing means 70 comprises a conduit 71 having upper and vent end 72 and a lower or discharge end 73. A pump or liquid forwarding means 74 is disposed within the line 71 adjacent the vent end 72. A plurality of regulated discharge means 75 is disposed at the discharge locations between the pump 74 and the discharge end 73. Beneficially the discharge means 75 are each individually controlled with a valve or flow restricting means 76. The embodiment of FIG. 4 is employed with particular advantage in relatively deep wells where substantial quantities of heat must be removed, and it is desired to maintain the temperature of the chamber such as the chamber 22 of FIG. 1 at a minimum, and substantial danger of liquid entrainment by the upwardly moving vapor exists. The liquid distributing means of FIG. 4 permits the low boiling liquid to be discharged at desired locations within the chamber without the danger of entrainment of a major portion of the liquid in the vapor in the upper portion of the chamber.

The method and apparatus of the present invention are further emminently satisfactory for maintaining permafrost conditions, many hundreds of feet and are satisfactory for establishing permafrost in areas wherein the soil is poorly consolidated.

As is apparent from the foregoing specification, the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention.

What is claimed is:

1. A method for maintaining permafrost about a well bore, the steps of the method comprising providing a conduit extending downwardly in the earth through a permafrost layer,

surrounding the conduit at least in the upper region of the permafrost with a thermally insulating layer, disposing generally about the insulating layer a hollow elongate housing defining therein a chamber, disposing within the chamber a liquid at a plurality of vertically spaced pre-selected locations within the chamber, the liquid boiling at least 0.lF. below the freezing point of the permafrost, removing a heated vapor upwardly through the tubing thereby heating the liquid within the elongate chamber to its boiling point,

condensing the liquid at a location generally adjacent the upper surface of the permafrost and returning the liquid downwardly within the chamber.

2. The method of claim 1 wherein the low boiling liquid is condensed in a condenser cooled by ambient air.

3. The method of claim 2 wherein the condensation of the liquid is by ambient air for a portion of a season and mechanical refrigeration for the remainder of the material. season. 5. The method of claim 4 wherein the cryogenic ma- 4. The method of claim 1 wherein during at least a terial is liquefied natural gas or liquid nitrogen. portion of a year the liquid is condensed by cryogenic 

1. A method for maintaining permafrost about a well bore, the steps of the method comprising providing a conduit extending downwardly in the earth through a permafrost layer, surrounding the conduit at least in the upper region of the permafrost with a thermally insulating layer, disposing generally about the insulating layer a hollow elongate housing defining therein a chamber, disposing within the chamber a liquid at a plurality of vertically spaced pre-selected locations within the chamber, the liquid boiling at least 0.1*F. below the freezing point of the permafrost, removing a heated vapor upwardly through the tubing thereby heating the liquid within the elongate chamber to its boiling point, condensing the liquid at a location generally adjacent the upper surface of the permafrost and returning the liquid downwardly within the chamber.
 2. The method of claim 1 wherein the low boiling liquid is condensed in a condenser cooled by ambient air.
 3. The method of claim 2 wherein the condensation of the liquid is by ambient air for a portion of a season and mechanical refrigeration for the remainder of the season.
 4. The method of claim 1 wherein during at least a portion of a year the liquid is condensed by cryogenic material.
 5. The method of claim 4 wherein the cryogenic material is liquefied natural gas or liquid nitrogen. 